The present techniques generally relate to novel phosphor compositions. More specifically, the present techniques describe phosphors that retain a substantial portion of their room temperature quantum efficiency at elevated temperatures. The phosphors may be used in light emitting diodes, Hg-based fluorescent lamps, gas discharge lamps, in UV, violet and/or blue lasers, as well as other white or colored light sources for different applications.
A phosphor is a luminescent material that absorbs radiation energy in one portion of the electromagnetic spectrum and emits energy in another portion of the electromagnetic spectrum. One important class of phosphors includes crystalline inorganic compounds of very high chemical purity and of controlled composition, to which small quantities of other elements, called “activators,” have been added for fluorescent emission. With the right combination of activators and inorganic compounds, the color of the emission of these crystalline phosphors may be controlled. Most useful phosphors emit radiation in the visible portion of the electromagnetic spectrum in response to excitation by electromagnetic energy outside the visible range. For example, phosphors have been used in mercury vapor discharge lamps to convert the ultraviolet (UV) radiation emitted by the excited mercury to visible light. Further, phosphors may be used in light emitting diodes (LEDs) to generate colors that may generally not be obtained from the LED chip itself.
Light emitting diodes (LEDs) are semiconductor light emitters that may be used as replacements for other light sources, such as incandescent lamps. They are particularly useful as display lights, warning lights and indicating lights or in other applications where colored light is desired. The color of light produced by an LED is dependent on the type of semiconductor material used in its manufacture.
Colored semiconductor light emitting devices, including light emitting diodes and semiconductor lasers (which are both generally referred to herein as LEDs), have been produced from Group III-V alloys such as gallium nitride (GaN). To form the LEDs, layers of the alloys are typically deposited epitaxially on a substrate, such as silicon carbide or sapphire, and may be doped with a variety of n- and p-type dopants to improve properties, such as light emission efficiency. With reference to the GaN-based LEDs, light is generally emitted in the UV to green range of the electromagnetic spectrum. Until quite recently, LEDs have not been suitable for lighting uses where a bright white light is needed, due to the inherent color of the light produced by the LED.
However, techniques have been developed for converting the light emitted from LEDs to useful light for illumination and other purposes. In one technique, the LED may be coated or covered with a phosphor layer. By interposing a phosphor excited by the radiation generated by the LED, light of a different wavelength, such as in the visible range of the spectrum, may be generated. Colored LEDs are often used in toys, indicator lights and other devices. Manufacturers are continuously looking for new colored phosphors for use in such LEDs to produce custom colors and higher luminosity.
The production of light from LEDs and other light sources generates heat as a byproduct. Phosphors may respond to this heat with a decrease in quantum efficiency, which is the number of photons emitted by the phosphor versus the number of photons absorbed by the phosphor. Accordingly, as the quantum efficiency of different phosphors may change at different rates as temperature increases, the light emitted by the device may dim or the color may shift as the device enters steady state operation.
Thus, there is a continued demand for phosphor compositions that may be used as components, individually or as part of a phosphor blend, in the manufacture of LEDs and other light sources. Such phosphor compositions should allow a wider array of light sources with desirable properties including good color quality (CRI>80), a large range of color temperatures, and a relative insensitivity to temperature changes.